The present invention relates generally to controlling brakes on a train of railcars, and more particularly to highly efficient, unitized railcar brake equipment that is based on electronic control of a pneumatically operated, stand-alone brake cylinder that can have a small, integrated air supply volume.
Historically, braking on railcars can has been implemented using pneumatic brake equipment provided on each railcar. Such prior art equipment typically can include a control valve which is connected to a brake pipe that interconnects the locomotive and each railcar in the train. The brake equipment on each car further can include a two compartment reservoir of pressurized air which the control valve can utilize to pressurize the brake cylinder on the car.
U.S. Pat. No. Re. 30,408, reissued Sep. 30, 1981, to the assignee of the present application, discloses railway brake apparatus including a brake cylinder device and a control valve device. The usual air reservoirs associated with conventional pneumatic brake equipment can be minimized or eliminated in the disclosed apparatus in favor of storing the compressed air within the brake cylinder device itself. The brake cylinder device disclosed embodies a pair of tandem-connected pistons of unequal diameter, the larger piston cooperating with the brake cylinder body to form on the respective opposite sides of this piston two chambers that are charged with compressed air via the train brake pipe, and in which chambers the air required for use by the brake apparatus, including the brake cylinder device, is stored. The aforementioned control valve device operates in response to variations in the train brake pipe pressure to control the transfer of air stored in the brake cylinder device, so as to develop differential forces across the respective pistons thereof and thereby effect a brake application and brake release. In addition to the, typical packing cup type pressure seals associated with the respective pistons of this brake cylinder device, there are several additional areas in which dynamic sealing is required, all of which are critical in the sense that leakage thereat affects the desired operation of the brake cylinder device. Further, passageways are required in the body of the brake cylinder device to conduct pressure between the control valve device and brake cylinder operating components. It is well known that the expense in the manufacture of a casting increases with the complexity in the configuration of these passages, as well as in the shape of the casting itself.
U.S. Pat. No. 4,418,799, issued Dec. 6, 1983 to the assignee of the resent application, discloses a pneumatic brake cylinder device which improves upon the brake cylinder device disclosed in Re 30,408. This brake cylinder device employs a pair of different sized fluid motors, the pressure chambers of which serve as air storage reservoirs. The cylinder of the larger fluid motor is formed by the main casting and contains a larger piston, while the cylinder of the smaller fluid motor is mounted to the main casting in coaxial relationship with the larger cylinder and contains a smaller piston having an elongated hollow body that is connected at its open, end to one side of the larger piston to form a pressure chamber therebetween. The smaller, positioning piston fits within the smaller cylinder in spaced-apart relationship therewith to form a pressure chamber delimited by a seal fixed on the main casting for engagement with the piston periphery at any point along its longitudinal axis. The larger, power piston cooperates with the larger cylinder to form pressure chambers on opposite sides thereof. As compared to the device disclosed in Re 30,408, the arrangement in U.S. Pat. No. 4,418,722 provides for a design employing fewer seals and a simplified main casting in which all the passages to the respective pressure chambers are contained. A similarity between the two devices is that a pair of pistons are employed, wherein the smaller piston displaces the larger piston in order to provide a brake application. As the smaller, positioning piston drives the larger, power piston air is transferred from an air chamber behind the power piston into a chamber on top of the positioning piston. In an emergency application, air in the chamber behind the power piston can be vented while air from a third chamber is coupled to the chamber on top of the positioning piston. To release the brakes, the chamber on top of the positioning piston is vented and the chamber behind the power piston is recharged.
Railcar brake equipment including the two brake equipment devices described above, historically initiate brake application and release operations on the railcar based upon pneumatic brake commands from a brake control valve on a locomotive. These pneumatic commands are typically communicated to each railcar by causing pressure changes in a brake pipe connecting each railcar to the locomotive brake control valve. In the past, and particularly on freight cars operating in North America, the railcar brake equipment, including the specific brake equipment described above, can only implement a xe2x80x9cdirectxe2x80x9d release of brakes on the railcar. Direct release means that the pressure in the brake cylinder on the railcar can only be fully released, as opposed to gradually releasing the pressure to gradually reduce the braking force. However, some pneumatically operated brake equipment has been disclosed which can provided graduated release capability. Additionally, graduated release of railcar brakes has recently been the target of brake system development in the American railway system and can be implemented using what is commonly referred to today as electrically controlled pneumatic (ECP) braking systems. ECP braking systems use specialized equipment on locomotives and railcars whereby brake command signals are generally instantaneously communicated, via a hardwired trainline or RF communications, between the locomotive and each railcar. The ECP brake equipment on each railcar typically utilizes solenoid type valves to control the air pressure in the brake cylinders, and are thus easily controllable to gradually increase or decrease the level of braking on each railcar. However, use of ECP braking systems can require a trainline, wire or RF communication equipment and electronic control valves on each railcars, as well as electronic control systems on the locomotive.
An efficient, unitized railcar brake equipment can be provided wherein a pneumatically operated, stand-alone brake cylinder can have a relatively small, integrated air supply volume which can be selectively coupled to opposite sides of a single piston for gradually applying or releasing the brakes on the railcar. The unitized brake equipment can be operated without, or independently of, a conventional pneumatic control valve, and can be controlled from a locomotive in an ECP manner using, for example, a trainline or an RF communication system. Furthermore, the unitized brake equipment could automatically initiate a full pneumatic brake application responsive to a loss of brake pipe pressure, without electronic intervention or control. The unitized brake equipment can include a brake cylinder and a piston member housed therein with a first air chamber in communication with the face of the piston and a second air chamber in communication with the opposite side of the piston. An air reservoir can also be provided, and can be formed as an integral part of the brake cylinder. The first and second air chambers and the air reservoir can be interconnected by air passages and controlled by valves, so that they may be selectively coupled and uncoupled to control pressure in the brake cylinder. Some of the valves can be electrically operated remotely, for example, by a train engineer, to control air pressure in the brake cylinder to operate the brakes on the railcar. Additionally, some valves can be configured to operate automatically in response to fluid pressure conditions prevailing in the air passages in the unitized brake equipment, or pressure conditions in the brake pipe, to which the unitized brake equipment can be connected. The unitized brake equipment can be supplied with pressurized air from, for example, the brake pipe for charging the reservoir and/or the first and second air chambers. Additionally, the unitized brake equipment can be selectively vented to the atmosphere, for example, by appropriate valves, for reducing the pressure in the brake cylinder. The valves for controlling the air pressure in the various chambers and reservoir can be provided as components of an electronic control valve portion, which can be mounted on the front or rear of the brake cylinder, via a pipe-bracket type of interface. The interface can be a separate component or can be formed as an integral part of the brake cylinder.
The unitized brake equipment can employ a xe2x80x9cself-actuatingxe2x80x9d brake cylinder, wherein air pressure is admissible to both sides of the piston, but acts on unequal effective areas provided on the opposing sides. For example, the face of the piston can be provided with a larger effective area such that it has an effective advantage over the opposite side of the piston. The unitized brake equipment can be designed such that, in release position, the internal volume of the first chamber, acting on the face of the piston, is relatively small, whereas the largest portion of the internal volume of the brake cylinder can be provided as the second chamber, which acts on the opposite side of the piston. The second chamber can thus also be utilized as an integrated air reservoir. To apply the brakes, the piston is forced to the applied position simply by connecting the air chambers on either side of the piston, and allowing the pressure on the face of the piston to approach the pressure on the opposite side, due to the area advantage. To thereafter reduce pressure in the brake cylinder, the smaller first air chamber acting on the face of the piston can be controllably exhausted to the atmosphere. Because much of the volume of air stored on the opposite side of the piston is simply transferred to the face of the piston in moving the piston to apply the brakes, only a relatively small volume of air is left on the opposite side of the piston when piston travel is completed and the brakes are fully applied. Thereafter, the pressure of this small volume can easily be incrementally increased or reduced, to gradually apply or release braking force by any degree desired, while using relatively little compressed air.
Other advantages of the unitized brake equipment over conventional ECP (all electric) controlled brake equipment can, in some instances result in reduced cost, size and weight. Further advantages can include simplified piping and installation, higher braking force capability from a given initial pressure, reduced consumption of pressurized air, and faster train charging and recharging. With the unitized brake equipment, the separate air storage or supply reservoirs and associated piping used with conventional railcar brake equipment can be eliminated, as can be the separate pipe bracket.